1. Field of the Invention
The present invention relates to a device for specific inhalation challenges, especially bronchial provocation tests, and to its method of use. The invention also relates to an improved generator of aerosol particles for use within the field of this invention.
2. Brief Description of the Prior Art
Occupational asthma is a common respiratory ailment. The diagnosis involves a combination of tools. Questionnaires were once the only means of diagnosis available. They were used to obtain an original description of occupational asthma among grain handlers by Ramazzini in 1700 (Raffle PAB, Lee WR, McCallum R1, Murray R. Hunter's Diseases of Occupations. 1st ed. Boston: Little, Brown and Cie, 1987, p 34-8), and among isocyanate workers, isocyanates being currently the most common causal agent. The presence of asthma can be confirmed by assessing spirometry and/or non-specific bronchial responsiveness. Immunological tests (skin tests, specific antibody tests) can confirm that there is sensitization to some agents, although they do not prove that the sensitization results in asthma. More recently serial monitoring of peak expiratory flow rates and bronchial responsiveness have been proposed for the diagnosis of occupational asthma.
Specific inhalation challenges carried out in the laboratory are still regarded as the gold standard for confirming the relationship between exposure to the suspected agent and the onset of asthma. In this experimental approach subjects are first exposed to a control product and, subsequently, to the occupational agent, in a controlled way. This procedure was first proposed by Pepys (Pepys J., Hutchcroft BJ., Bronchial provocation tests in etiologic diagnosis and analysis of asthma. Am Rev Respir Dis 1975; 112:829-59) and many new causes of occupational asthma have been identified using this method. For suspected agents available in powder form, subjects are asked to tip the product from one tray to another in a challenge room. There are several pitfalls to this procedure:
1. Subjects may be exposed to high concentrations of particles, resulting in unduly severe episodes of bronchoconstriction (Cartier A, Malo JL, Dolovich J. Occupational asthma in nurses handling psyllium. Clin Allergy 1987; 17:1-6). The concentration of particles may be higher than the standard, TLV-STEL (threshold limit value-short term exposure level), the concentration to which workers can be exposed continuously for short periods of time without suffering toxic effects. This may result in non-specific irritant reactions.
2. Exposure is erratic; the subject is exposed to high concentrations at times and acceptable levels at other times.
3. It is difficult to draw a proper dose-response curve since the concentration of particles cannot be precisely determined.